topic Re: why multiple ampersand resolve to this? in SAS Programming

why multiple ampersand resolve to this?

ZRick — Tue, 10 Apr 2012 06:07:34 GMT

%let var=city;

%let n=6;

%put &&&&var&n;

after 4 ampersand, and resolve to &var6, why &var?

I mean it should be &city6.right?

Re: why multiple ampersand resolve to this?

shivas — Tue, 10 Apr 2012 06:43:55 GMT

Hi,

Two &s (&&) resolve to one &

Four or more &s are resolved from left to right.

So if you want &city6 then you need to use &&&&&var&n.

Thanks,

Shiva

Re: why multiple ampersand resolve to this?

Ksharp — Tue, 10 Apr 2012 07:13:03 GMT

Here is process:

&& &&var&n

-> & &var6

-> &var6

Ksharp

Re: why multiple ampersand resolve to this?

Astounding — Tue, 10 Apr 2012 13:02:24 GMT

ZRick,

If you are looking to get &city6, while 4 ampersands work, 3 would have been enough.

In &&&var&n:

&& becomes &

&var becomes city

&n becomes 6

So the whole thing becomes &city6

Many times, extra ampersands don't hurt but they merely require additional resolution. For example, 6 ampersands would also have worked if you add a delimiter (see below).

In &&&&&&var.&n

&& becomes &

var. remains var.

&n becomes 6

So after one set of resolutions, this becomes &&&var.6

In the next set of resolutions,

&& becomes &

&var. becomes city

6 remains 6

So after the second set of resolutions, this becomes &city6

As other posters mentioned, move from left to right, and resolve each text string. Then re-resolve if necessary.

Good luck.

Re: why multiple ampersand resolve to this?

ZRick — Wed, 11 Apr 2012 03:42:52 GMT

Astounding,

Can you explain why adding period then whole result changed? if I put %put &&&&var.&n; now it turns to city6, why is that?

Re: why multiple ampersand resolve to this?

manojinpec — Wed, 11 Apr 2012 04:10:25 GMT

Hi,

. will tell sas that the macro resolution shoudl end at dot and after that any resolution would be different from the current.

Re: why multiple ampersand resolve to this?

Ksharp — Wed, 11 Apr 2012 05:52:19 GMT

Here is process:

&& &&var.&n

-> & &var.6

-> &var.6

-> city6

Ksharp

Re: why multiple ampersand resolve to this?

Astounding — Wed, 11 Apr 2012 13:29:21 GMT

That's absolutely correct. To put it in words ...

With a dot, the expression resolves as Ksharp indicated. Within &var.6, the dot delimits the name of the macro variable. It tells macro language that VAR is the name of the macro variable, and 6 is just text to be appended to &VAR.

Without a dot, the expression would resolve to &var6. How would macro language know to look for &VAR, rather than &VAR6? It doesn't. This would trigger a search for &VAR6. Since there is no such macro variable, it would generate an error.

In general, keep asking! Speaking for myself only, I'm more than willing to help when I see that you are putting in the work and trying hard to learn.